Fix test_callout to dispatch via filter's bound calloutKey + add bind_ipv6 helper

[mikeagun]

Description

Add support for multiple callouts per layer, add IPv6 bind callout, and populate additional bind callout fields.

Problem

fwp_engine_t::test_callout() looks up the callout by layer alone via get_callout_key_from_layer_guid_under_lock(), which returns the first fwpm_callouts entry matching the layer.

• Real WFP dispatches each filter to the specific callout it's bound to via action.calloutKey. usersim already records that binding during add_fwpm_filter (see src/fwp_um.h:140) — test_callout just discards it.
• The behavior is non-deterministic when more than one callout is registered at the same WFP layer, which is a normal pattern in real WFP and blocks tests for any project that does it.

Fix

Look up the callout via the filter's bound action.calloutKey instead of scanning by layer:

  -        const GUID* callout_key = get_callout_key_from_layer_guid_under_lock(&layer_guid);
  -        if (callout_key == nullptr) {
  -            return FWP_ACTION_CALLOUT_UNKNOWN;
  -        }
  -        callout = get_callout_from_key_under_lock(callout_key);
  +        callout = get_callout_from_key_under_lock(&fwpm_filter->action.calloutKey);

For tests with one callout per layer (today's status quo) the behavior is identical. For tests with multiple callouts per layer it now matches real WFP.

Additional changes (related, small).

• Add usersim_fwp_bind_ipv6() mirroring the existing usersim_fwp_bind_ipv4().
• In test_bind_ipv4 / test_bind_ipv6, populate COMPARTMENT_ID, IP_LOCAL_INTERFACE, and ALE_USER_ID incoming values. These are read by sock_addr-style bind callbacks but ignored by the legacy bind callback, so the addition is non-breaking.

Motivation. This surfaced while adding a BPF_PROG_TYPE_CGROUP_SOCK_ADDR bind hook (BPF_CGROUP_INET4/6_BIND) to eBPF for Windows, which coexists with the existing legacy bind hook at FWPM_LAYER_ALE_RESOURCE_ASSIGNMENT_V4/V6. Without this fix, unit tests can't reliably target one callout vs. the other when both are registered.